Solar regions active

Top: Jules Janssen (1885). Bottom: Hinode’s Broadband Filter Imager (2009)

Photograph of an active region, taken by Jules Janssen on 22 June 1885 at the Observatoire de Meudon (Paris, France). In addition to the - spots and pores of the active region, the granulation pattern of the solar surface can clearly be seen. The photograph recorded a very large feld of view, and parts of it appear blurred because of the efects of atmospheric January 4: turbulence. Peak of Quadrantids meteor shower (08:20 GMT)

The lower panel shows active region 11029 as observed by the Hinode sa- January 13-15: nd tellite on 27 October 2009 near the edge of the solar disk. The image quality 2 NCSP DKIST Data Training Workshop, is homogeneous over the entire feld of view because the measurements are California State University, Northridge, USA not afected by the Earth atmosphere. As usual, one of the spots forming the January 21: active region is larger and more stable than the other, which appears frag- EAST General Assembly, Prague, Czech Republic mented into many small pores.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar granulation

Top: Jules Janssen (1890). Bottom: Swedish 1m Solar Telescope (2004)

The image at the top is a particularly good example of early photo- graphs of the solar granulation. It was taken by Jules Janssen at the Obser- vatoire de Meudon (France) on 11 October 1890, from a projection of the solar disk measuring 1.2 meters in diameter. The photograph captured the granulation pattern of the solar surface with surprising detail. However, the February 3-7: feld of view is so large that parts of the image appear blurred by turbulence 5th Asia Pacifc Solar Meeting, Pune, India in the Earth’s atmosphere. February 5: The CCD image at the bottom shows the solar granulation as seen by the Swe- Solar Orbiter Launch, Cape Canaveral, USA dish 1-m Solar Telescope on La Palma (Spain) on 22 August 2004. The obser- February 11: vations were acquired using adaptive optics and subsequently reconstructed International Day of Women and Girls in Science with sophisticated techniques to reach the difraction limit of the telescope. In addition to granules and intergranular lanes, one can observe tiny bright points that represent small-scale magnetic felds on the solar surface.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar flares

Top: Richard C. Carrington (1859). Bottom: Hinode’s Broadband Filter Imager (2007)

Original drawing of the frst detection of a solar fare (top). “I had secured diagrams of all the groups and detached spots, […] when two patches of intensely bright and white light broke out, in the positions indicated in the ap- pended diagram by the letters A and B, and of the forms of the spaces left white. My frst impression was that by some chance a ray of light had penetrated a hole March 20: in the screen [...], for the brilliancy was fully equal to that of direct sun-light.” Spring Equinox (03:50 GMT) Carrington, MNRAS, 20, 13 (1859). March 23-27: st The image at the bottom shows an X 3.4 class fare observed by the Hinode 1 Parker Solar Probe Meeting, Laurel, USA satellite in a complex active region on 13 December 2006. Hinode recorded March 31- April 1: the fare through a Ca II H flter, which samples the solar chromosphere. The SOLARNET Public Engagement Training Workshop, extreme brightening is due to energy released by the reconnection of mag- Northumbria University, UK netic feld lines.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar spectroscopy

Top: John Evershed (1918). Bottom: Hinode’s Spectro-Polarimeter (2006)

Photograph of the solar intensity spectrum taken by John Ever- shed at Kodaikanal Observatory (India) on 20 November 1918. The vertical dark lines are spectral absorption lines created by the diferent chemical ele- ments present in the solar atmosphere. The horizontal dark band is a sun- spot. Spectral lines are slightly tilted at the position of the , due to March 31 - April 1: the existence of horizontal gas motions in the sunspot penumbra – known SOLARNET Public Engagement Training Workshop, as Evershed fows. Northumbria University, UK

The lower panel shows modern spectroscopic measurements by the spec- April 22: tropolarimeter aboard the Hinode satellite. The data were taken on 13 De- Peak of Lyrids meteor shower (07:00 GMT) cember 2006 at the position of a faring sunspot. The spectrum on the right April 23: displays the four polarization states of the light in two iron lines at 630 nm. Peak of Pi Puppids meteor shower (12:00 GMT) The spectral resolution of these observations is much higher than that of the spectrum taken by Evershed.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Active region prominences

Top: Lorenzo Respighi (1870). Bottom: Hinode’s Broadband Filter Imager (2007)

Prominences observed by Lorenzo Respighi in 1870 at the border of the solar disk near the position of active regions (top). These detailed draw- ings show the wide range of shapes and sizes of active region prominences. The observations were made using spectroscopic techniques, which were very advanced in Italy at that time. Active region prominences are smaller, May 3-8: shorter, and more dynamical than quiescent prominences occurring far from EGU General Assembly, Vienna, Austria . May 5: The lower image shows an active region prominence observed by the Hinode Peak of Eta Aquariids meteor shower (21:00 GMT) satellite on January 12, 2007. The measurements were taken in the H line of ionized calcium. The prominence exhibits delicate threads that are believed to trace the chromospheric magnetic feld. It shows a very rapid evolution, changing shape constantly. The sunspot associated with the prominence can be seen as a dark feature near the right border of the image.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar prominences

Angelo Secchi (1872)

Prominences observed by Father Angelo Secchi in July 1872 at the border of the solar disk. The measurements were made using spectro- scopic techniques, which allowed astronomers to see the prominences out of total solar eclipses. Indeed, spectroscopy made it possible to monitor the solar limb daily in search for prominences and other solar phenomena. Their June 14-19: number was found to vary in phase with the solar cycle. Prominences were SPIE Astronomical Telescopes, Yokohama, Japan thought to be eruptions of the chromosphere, coming in diferent shapes and sizes. Secchi proposed a complex classifcation consisting of several June 20: groups. Summer Solstice (21:43 GMT) June 21: Due to their strong emission in chromospheric lines, notably the H-alpha line, Annular prominences were soon considered to be made of hot gas. This view stands today, although we also know that prominences are much cooler than the June 22-26: coronal plasma where they are embedded. Cool 21, Toulouse, France

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar filaments

Top: Observatoire de Meudon (1909). Bottom: ChroTel (2011)

The photograph on top is one the frst H-alpha spectroheliograms re- corded at Observatoire de Meudon (Paris, France). Taken on 15 June 1909, it shows the chromosphere of the Sun. The dark long structures visible on the solar disk are flaments. When observed at the limb, flaments are called prominences and appear bright. July 5: Penumbral lunar eclipse The CCD image at the bottom shows the solar chromosphere in H-alpha as recorded by the Chromospheric Telescope (ChroTel) on 15 November 2011. July 27-30: Both dark flaments and bright prominences can be seen. The much high- Waves and Instabilities in the Solar Atmosphere, er contrast is partly due to the application of new image processing tech- Newcastle, UK niques. ChroTel observes the full disk of the Sun at 3 diferent wavelengths: July 28-31: H-alpha, Ca II K, and He I 1083 nm. This small robotic telescope is located at Hinode-14 Science Meeting, Washington DC, USA the Observatorio del Teide on Tenerife (Spain) and was developed by the KIS (Germany) and HAO (USA).

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Sunspot penumbra

Top: Samuel Langley (1873). Bottom: Goode Solar Telescope (2015)

The image at the top is a remarkable drawing of a sunspot created by Samuel Langley in December 1873, using the 13-inch Fitz-Clark refractor of the Allegheny Observatory (Pennsylvania, USA). It shows a very detailed view of the flamentary structure of the sunspot penumbra. Bundles of in- dividual flaments can be seen protruding into the dark umbra. Penumbral August 12: flaments are extremely narrow, so excellent atmospheric conditions had to Peak of Perseids meteor shower (10-13 GMT) occur for Langley to identify them. August 15-23: The lower image shows penumbral flaments in extraordinary detail, as ob- 43rd COSPAR Scientifc Assembly, Sydney, Australia served with the 1.6-m Goode Solar Telescope at Big Bear Solar Observatory (California, USA) on 20 June 2015. At high spatial resolution, penumbral August 25-29: flaments exhibit central dark cores and bright heads. Scientists still debate IAU Symposium 365, Dynamics of Solar and Stellar the origin of penumbral flaments and their relation to the sunspot mag- Convection zones and Atmospheres, Moscow, Russia netic feld.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar spicules

Top: Angelo Secchi and Pietro Tacchini (1874). Bottom: Hinode Broadband Filter Imager (2007)

Solar spicules were discovered by Angelo Secchi in the 19th cen- tury, observing the Sun by spectroscopic means. He called them “prateria ardente”, which means “burning feld” in Italian. The image at the top shows careful drawings of spicules and small prominences on the solar limb done by Angelo Secchi and Pietro Tacchini in 1874. By that time, systematic ob- September 7-11: servations of the solar limb were made daily in , Palermo and Padova 16th European Solar Physics Meeting, Turin, Italy (Italy), recording incredible detail. September 22: The lower image shows high-resolution observations of spicules taken by Autumn equinox (13:31 GMT) the Japanese Hinode satellite on 8 November 2007. The Broadband Filter Imager was used to study the rapid evolution of spicules at the solar limb in the Ca II H spectral line. Spicules are ubiquitous jets of plasma in the chromo- sphere, but their origin is not fully understood.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar prominences

Right: Angelo Secchi (1871). Left: Hinode’s Narrowband Filter Imager (2007).

Solar prominence observed by Father Angelo Secchi at Collegio Romano (Rome, Italy) in 1871. Secchi studied the fne structure of promi- nences, estimated their size, and hypothesized about their nature. He also recognized the link between sunspots, faculae and prominences, reporting that “it is certainly a great fact that there are never spots without faculae. And October 8: now we know that the spots and the faculae are accompanied by diference Peak of Draconids meteor shower (12:30 GMT) in height in the photosphere and by luminous jets” - prominences. October 12-16: The image on the left shows a prominence observed by the Hinode satellite 2020 SDO Science Workshop, Vancouver, Canada in the center of the H-alpha line on 25 April 2007. The H-alpha observations October 21: sample gas at chromospheric temperatures. The delicate fne details of the Peak of Orionids meteor shower (05:30 GMT) prominence are very noticeable, as is the large dark cavity that forms at its base. Some of these features were already observed by Secchi and other fel- low astronomers.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar corona

Left: Total solar eclipse of 2010. Right: Total solar eclipse of 1860.

Angelo Secchi organized a scientifc expedition to Desierto de Las Palmas (Spain) to observe the total solar eclipse of 18 July 1860. The photo- graphs he took showed prominences at the edge of the solar disk (the red- dish features visible on the right panel) and much longer coronal streamers. The same prominences were observed by Warren De La Rue from Rivabe- November 12: llosa, 500 kilometers away from Secchi’s site. This demonstrated that promi- Peak of Northern Taurids meteor shower (05:00 GMT) nences were indeed solar features and not optical illusions. November 17: The left panel displays the solar corona as recorded by an international team Peak of Leonids meteor shower (11:00 GMT) in Tatakoto Atoll (French Polynesia) during the total eclipse of 11 July 2010. November 30: Coronal loops and streamers can be seen with incredible detail. This view of Penumbral lunar eclipse the corona is possible thanks to the combination of photographs with difer- ent exposure times and the application of sophisticated image processing techniques.

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Solar telescopes

Top: Christoph Scheiner’s telescope (circa 1625). Bottom: European Solar Telescope (2027).

Telescope used by Christoph Scheiner to trace sunspots in Rome (Italy) around 1625. The image of the Sun created by the instrument was pro- jected on a screen, over which sunspots could be drawn accurately. Schei- ner’s telescope was a small refractor made up of lenses. The illustration is from the book “Rosa Ursina” by Scheiner. December 14: Total solar eclipse The lower image shows a rendering of the future European Solar Telescope (EST). With a primary mirror of 4 meters, it will be the largest telescope ever December 14: built in Europe. The EST consortium has proposed to install it at Observato- Peak of Geminids meteor shower (00:50 GMT) rio del Roque de Los Muchachos on La Palma (Spain). Construction will start December 14-20: towards the end of 2021. The EST design is optimized to study the magnetic Dynamic Sun III, Villarrica, Chile and dynamic coupling of the solar atmosphere through multi-wavelength observations. EST will be equipped with state-of-the-art instrumentation, in- December 21: cluding spectropolarimeters based on integral feld units. Winter solstice (10:02 GMT)

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The European Solar Telescope (EST) is the next step in the European quest for a better understanding of the Sun Hinode (ISAS/JAXA,Bottom: Hinode NAOJ, NASA,STFC, ESA) chive, EVER/A/1/E203 Top: The MuseumGroup, Science Evershed John Ar- spectroscopy Solar (ISAS/JAXA,Bottom: Hinode NAOJ, NASA,STFC, ESA) Malherbe Jean-Marie Observatoire deMeudon.Courtesy Top: solaires”, JulesJanssen,“Études dessurfaces regions active Solar Courtesy Dick Shine(LMSAL) Dick Courtesy (ISAS/JAXA, Hinode Left: NAOJ, NASA,STFC, ESA). IlariaErmolliandMarcoCourtesy Ferrucci (INAF-OAR) Astronomico INAFOsservatorio diRoma. Right: prominences Solar Carsten Denker (AIP) Bottom: Christoph Kuckein, MeetuVerma, Malherbe.Jean-Marie Top: ObservatoiredeMeudon.Courtesy filamentsSolar

OCTOBER JULY APRIL JANUARY Habbal, Vojtech Rušin Druckmüller, Dietzel, Miloslav Left: Shadia Martin Ilaria Ermolli(INAF-OAR) ©INAF.Right: Tra Secchi, Angelo CieloeTerra. Courtesy corona Solar Observatory, USA) WendaBottom: Courtesy Cao Solar (BigBear (www.codex99.com/illustration/119.html) Top: JimHughes Courtesy penumbraSunspot Luis Rubio Bellot (IAA-CSIC) Courtesy (ISAS/JAXA,Bottom: Hinode NAOJ, NASA,STFC, ESA). IlariaErmolli,MarcoCourtesy Ferrucci (INAF-OAR) Top: ©INAFMuseoAstronomico Copernicano. prominences Active region van derVoort (ITA) (ISP) andLuc vanBottom: Michiel Rouppe Noort Malherbe Jean-Marie Top: ObservatoiredeMeudon.Courtesy granulationSolar

NOVEMBER AUGUST MAY FEBRUARY Hinode (ISAS/JAXA,Bottom: Hinode NAOJ, NASA,STFC, ESA) Astronomical Society, 20,13(1859) Top: Carrington, Richard MonthlyNotices oftheRoyal flares Solar EST project. Courtesy Gabriel Pérez Gabriel Bottom: ESTproject. Courtesy (IAC) Library, Harvard University 1626, p. 150.Scanned from theoriginalatHoughton Top: From by “RosaUrsina sive Christoph Sol” Scheiner, telescopes Solar Joten Okamoto (NAOJ,Courtesy Japan) (ISAS/JAXA,Bottom: Hinode NAOJ, NASA,STFC, ESA). (4ASTRI,6725:5) sitätsbibliothek Göttingen NiedersächsischeStaats-undUniver-(1876). Courtesy Top: spicules Solar Universitätsbibliothek (4ASTRI,6725:14) Göttingen NiedersächsischeStaats-und (1872). Courtesy degliSpettroscopisti Italiani Memorie dellaSocietà prominences Solar Memorie della Società degli SpettroscopistiMemorie della Società Italiani

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